Nessi R, Castellana L, Paruccini N, Blanc M, Uslenghi C M
Istituto di Scienze Radiologiche, Università di Milano, Cattedra di Radiologia presso Ospedale S. Paolo.
Radiol Med. 1995 Sep;90(3):298-302.
The physical characteristics of radiographic images, namely spatial resolution and contrast, have obvious effects upon diagnostic image usefulness. We investigated the spatial resolution of both radiographs and magnified digital obtained with a storage phosphor system, in comparison with a film-screen combination. This study was carried out on the conventional radiographs of a phantom grid 0.5 mm thick, with resolution ranging from 0.5 to 10 lp/mm. Each examination was compared at naked eye and with the electronic evaluation of a region of interest on both standard and magnified views or by digitization with a charge coupled detector (CCD) television camera followed by the computing of the modulation transfer function curve. Our results demonstrate a higher spatial resolution of direct magnification, on both digital and film-screen pictures (over 5 lp/mm). On the contrary, the electronic magnification on the monitor yields the same spatial resolution as non-magnified digital images (up to 4.3 lp/mm). By selecting appropriate regions of interest, we could demonstrate the compression of the non-magnified images on the monitor. The modulation transfer curves show that direct magnification yields higher spatial resolution than electronic magnification and non-magnified views. Viewing electronically magnified images on the monitor yields the same resolution as contact radiographs: the monitor offers the advantage of an easier study of the regions of interest.
射线照相图像的物理特性，即空间分辨率和对比度，对诊断图像的效用有明显影响。我们研究了使用存储磷光体系统获得的X线照片和放大数字图像的空间分辨率，并与屏-片组合进行了比较。本研究是在一个厚度为0.5mm、分辨率范围为0.5至10lp/mm的体模格栅的传统X线照片上进行的。在肉眼观察以及对标准视图和放大视图上的感兴趣区域进行电子评估时，或者通过使用电荷耦合探测器（CCD）电视摄像机进行数字化处理，随后计算调制传递函数曲线，对每次检查进行比较。我们的结果表明，在数字图像和屏-片图像上，直接放大的空间分辨率更高（超过5lp/mm）。相反，显示器上的电子放大产生的空间分辨率与未放大的数字图像相同（高达4.3lp/mm）。通过选择合适的感兴趣区域，我们可以证明显示器上未放大图像的压缩情况。调制传递曲线表明，直接放大产生的空间分辨率高于电子放大和未放大视图。在显示器上查看电子放大图像产生的分辨率与接触式X线照片相同：显示器具有更便于研究感兴趣区域的优势。
